Update error for Microsoft security essential and iTunes

Hello friends,
I think there is a problem with the Windows 8 operating system. I tried to update antivirus Microsoft security essential I ended up in vein. There is a peculiar problem; I used to do it just like that. Today I discovered the same error message is for iTunes update too. Something is terribly wrong in my system. Urgent help please.

The installation failed.
The Installer encountered an error that caused the installation to fail. Contact the software manufacturer for assistance.
